This invention relates to airfoils, and more particularly to a laminar flow control swept wing for use on jet transports.
There have been continuing efforts over the years to reduce the aerodynamic drag of aircraft and their components in order to increase cruise efficiency. It is known by those skilled in the art that if the boundary layer airflow over an airfoil can be maintained laminar, skin friction drag is minimized.
Use of suction applied to aerodynamic surfaces to maintain laminar flow at high Reynolds numbers and during flight conditions beyond those where laminar flow can be expected to occur naturally, is also well known to those skilled in the art. There have been many proposals to accomplish this using various slot arrays, perforated or porous skin and associated suction ducting.
However, there are generally disadvantages associated with suction systems as previously proposed, such as undue added structural weight, complexity, and increased construction and maintenance costs. Additionally, since the use of suction on aerodynamic surfaces involves the addition of new systems, parts, substructures and structures that must integrated with the principal airflow systems and structures, the task of establishing functional reliability of new and unproven arrangements required by prior proposals has been a major concern and deterrent.
Also, variability of the operating environment of the aircraft can impose conditions which are generally inhospitable to the maintenance of laminar flow over aerodynamic surfaces. The distribution and magnitude of applied suction is based on certain assumptions as to operating environment, and when conditions vary widely as they do at times in flight due to air turbulence, noise, etc., those design assumptions no longer fit. The present invention, as one of its objectives, seeks to minimize drag penalty experienced when air conditions vary beyond assumed values.
Prior laminar flow control systems were predicted essentially on gross compromises of conventional wing construction and configuration so as to accommodate slots, pores, ducts, etc. The added cost, weight and complexities, along with the difficulties of access to inspect and maintain the added subsystems, tended to offset the gains sought through laminar flow control even under assumed (ideal) flight conditions.
An object of this invention is to provide a laminar flow control airfoil which minimizes the aforementioned limitations and disadvantages of prior system proposals and which can be incorporated in conventional proven wing structures with minimum interface problems and with essentially no disruption or interference with the design integrity and established reliability of the existing airfoil main structure and its systems.
It is another object of this invention to provide an airfoil structural arrangement that has a built-in capability to maintain surface smoothness in the critical nose area against dents, erosion, and accumulations of insects and dirt particles. These factors cause disturbances which inhibit or destroy laminar flow but which can be controlled by the proper use of leading edge suction.